Field of the Invention
The present invention provides for methods of preventing and/or treating S. aureus-associated bacteremia and sepsis, and methods for preventing and/or treating S. aureus-associated pneumonia in immunocompromised patients using anti-S. aureus alpha-toxin (anti-AT) antibodies.
Background Art
Staphylococcus aureus (S. aureus) is a leading cause of mortality and morbidity worldwide, causing a diverse array of infections ranging from mild skin and soft-tissue infections to serious invasive diseases such endocarditis, osteomyelitis, and necrotizing pneumonia (Lowy F D, N Engl J Med, 339(8): 520-32 (1998); Klevens et al, JAMA 298(15): 1763-71 (2007). S. aureus is commonly classified as either methicillin resistant (MRSA) or methicillin sensitive (MSSA). Several reports have shown that S. aureus infections result in serious outcomes regardless of resistance status (Fowler et al, Arch Intern Med. 163(17):2066-72 (2003); de Kraker et al, PLoS Med. October; 8(10):e1001104 (2011).
Antibiotics are standard of care for treating S. aureus disease. Despite the introduction of new antibiotics against S. aureus, emergence of new resistance mechanisms requires new approaches to prevent or treat S. aureus diseases. Prior to the antibiotic era, passive administration of immune sera to infected patients was used clinically to treat bacterial infections (Keller and Stiehm, Clin Microbiol Rev 13(4):602-14 (2000)). Today, similar methods are used to treat some toxin-mediated bacterial diseases (e.g., botulism, diphtheria, tetanus) (Keller and Stiehm, Clin Microbiol Rev 13(4):602-14 (2000); Arnon et al, N. Engl. J. Med. 354: 462-471 (2006). S. aureus alpha toxin (AT) has been shown to be a key virulence determinant (amongst numerous other extracellular factors) in several S. aureus disease models (e.g., dermonecrosis, pneumonia, sepsis, endocarditis, and mastitis) by comparing S. aureus strains deficient for AT expression with isogenic wild-type parent strains (Bramley et al, Infect Immun. 57(8):2489-94 (1989); Bayer et al, Infect. Immun. 65: 4652-4660 (1997); Kernodle et al, Infect. Immun. 65: 179-184 (1997); Bubeck Wardenburg et al, Infect Immun. 75(2):1040-4 (2007); Bubeck Wardenburg et al, J Exp Med. 205(2):287-94 (2008); Kobayashi et al, J Infect Dis. 204(6):937-41 (2011)).
AT is a cytolytic 33 kDa pore-forming toxin produced by 90% of S. aureus strains and is considered to be a major virulence factor. It is secreted as a monomer and binds the specific receptor ADAM-10 on target cell membranes (Wilke and Bubeck Wardenburg, PNAS 107(30):13473-8 (2010); Inoshima et al, Nat Med 17(10):1310-4 (2011). AT oligomerizes into a heptameric prepore and undergoes a conformational change resulting in transmembrane .beta.-barrel formation and subsequent cell lysis (Bhakdi and Tranum-Jensen, 1991; Song et al, 1996). Platelets, along with epithelial, endothelial, and immune cells (e.g., lymphocytes and macrophages), are susceptible to AT-lysis, suggesting the toxin has direct impact on tissue damage and immune evasion (Bhakdi and Tranum-Jensen, Microbiol Rev. 55(4):733-51 (1991); Ragle and Bubeck Wardenburg, Infect Immun. 77(7):2712-8 (2009); Tkaczyk et al, Clin Vaccine Immunol 19(3):377-85 (2012)). At sub-lytic concentrations, AT has also been demonstrated to exert significant cytotoxic effects (Grimminger et al, J Immunol. 159(4):1909-16 (1997); Wilke and Bubeck Wardenburg, PNAS 107(30):13473-8 (2010); Inoshima et al, Nat Med 17(10):1310-4 (2011)). AT binding and oligomerization on macrophage membranes activates the NLRP3 inflammasome that, along with other staphylococcal pathogen-associated molecular patterns (PAMPs), induces IL-1.beta. secretion and promotes cell death (Craven et al, PLoS One 4(10) (2009); Kebaier et al, J Infect Dis 205(5):807-17 (2012). Increased proinflammatory cytokine expression (e.g. IL-1.beta.) is a hallmark of acute lung injury (Goodman et al, Cytokine Growth Factor Rev. 14(6):523-35 (2003)).
AT also activates ADAM-10 mediated proteolysis of E-cadherin present in cell-cell adhesive contacts at sub-lytic concentrations, leading to a disruption in epithelium integrity and contributing to epithelial damage seen in pneumonia and skin and soft tissue infections (Inoshima et al, Nat Med 17(10):1310-4 (2011); Maretzky et al, PNAS 102(26):9182-7 (2005); Inoshima et al, J Invest Dermatol. 132(5):1513-6 (2012). AT exerts its cytotoxic effects through direct and indirect activities to create an environment conducive for bacterial growth and invasive disease. Consequently, targeted inhibition of AT could prevent or limit S. aureus-associated disease. This hypothesis is supported other studies which demonstrate reductions in S. aureus disease severity in murine infection models following active or passive immunization directed against AT (Menzies and Kernodle, Infect Immun 64(5):1839-41(1996); Bubeck Wardenburg et al, J Exp Med. 205(2):287-94 (2008); Ragle and Bubeck Wardenburg, Infect Immun 77(7):2712-8 (2009); Kennedy et al, J Infect Dis. 202(7):1050-8 (2010); Tkaczyk et al, Clin Vaccine Immunol 19(3):377-85 (2012)).
An anti-AT antibody having an Fc variant region and its parent antibody LC10 are human, high-affinity, anti-AT mAbs (previously disclosed in U.S. Prov. Appl. No. 61/440,581 and in Intl. Appl. No. PCT/US2012/024201 (published as WO2012/109205), the contents of each of which are herein incorporated by reference) and in Tkaczyk et al., Clinical and Vaccine Immunology, 19(3): 377 (2012).
Bacteremia and septic shock account for the majority of Staphylococcus aureus invasive disease (Klevens, et al, JAMA, 298(15): 1763-71 (2007). AT has been proposed to be an important virulence factor during S. aureus sepsis and to be responsible for endothelial damage during sepsis (Powers, et al, J Infect Dis. 206(3):352-6 (2012). Interaction of AT with its receptor on endothelial cells allows the toxin to mediate vascular damage by direct cell lysis or activation of ADAM-10-mediated proteolysis of endothelial tight junctions (Id.). Both mechanisms would increase vascular permeability, a hallmark of bacterial sepsis.
While passive immunization with anti-AT monoclonal antibodies has been shown to result in a significant increase in survival in a murine model of staphylococcal pneumonia as described in U.S. Prov. Appl. No. 61/440,581 and in Intl. Appl. No. PCT/US2012/024201, it is not known whether anti-AT antibodies are effective in increasing survival in immunocompromised mammals having S. aureus associated diseases. This is a critical piece to understand as immunocompromised individuals, particularly those suffering from neutropenia, are at increased risk for S. aureus infections (Andrews and Sullivan, Clin Microbiol Rev. 16(4):597-621 (2003); Bouma et al., Br J Haematol. 151(4):312-26 (2010)).
The present invention provides, for the first time, a demonstration that anti-AT antibodies are effective in prophylaxis in sepsis and in immunocompromised pneumonia.